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Climate mitigation options through Afforestation – The Forest Carbon Tool


The establishment of new forests has a highly significant role to play in addressing our climate challenges and ensuring we can build a significant future carbon sink by mid-century. Teagasc Forestry Specialist Tom Houlihan discusses this and the development and use of the Forest Carbon Tool

The establishment of new forests has a highly significant role to play in addressing our climate challenges and ensuring we can build a significant future carbon sink by mid-century. Teagasc Forestry Specialist Tom Houlihan and Dr Kevin Black of Forest Environmental Research and Services (FERS) Ltd presented on this topic on a recent Teagasc Signpost Series Webinar which took place on Friday, 9th April. The webinar also focused on the development and use of a recently-launched Forest Carbon Tool.

There are many good reasons for sustainably expanding our forest resource. There is also a clear and ongoing need for a balanced approach between achieving sustainable wood production and realising the social and environmental benefits that can be delivered by sustainable management in new and existing forests. Webinar viewers heard how all forest types (conifer, broadleaf and mixed forests) have a significant role to play in contributing to this wide range of ecosystem services required by society. Climate mitigation is an important example of such a service provided by new and developing forests and woodlands.

While there is increased ambition to incorporate native species and diversity in new planting enterprises, productive conifers are and will be required to meet a strong underlying demand for new homes and for other future uses. For example, a recent UK Timber Trade Federation webinar also featured predicted tight timber demands in 2021 with demand outstripping supply for some years to come. A balanced approach is, therefore, essential and prudent.

At forest level, carbon balances are based on net emissions or removals from 5 pools (reservoirs of carbon, figure 1). These consist of the above and below ground biomass pools, the litter pool, the deadwood pool and the soil carbon pool. There are ongoing and complex carbon transfers (fluxes) between these pools. Carbon dioxide (CO2) is taken out of the atmosphere and sequestered by trees during photosynthesis with a corresponding release of oxygen.  The rate of carbon uptake is affected by many factors, such as species, yield class, soil type, management activities such as harvesting and previous land use. There are processes such as long term allocation of carbon into above and below ground forest biomass and turnover of biomass into the soils and dead organic matter. There can also be loss of some carbon as a result of respiration by trees, both above and below ground, and decomposition (or oxidation) of soil organic matter.  Where carbon uptake exceeds loss as is the norm, the forest is a ‘sink’. Conversely, if loss exceeds uptake the forest is a ‘source’. The final output is the sum of the carbon stock changes.

Figure 1: Carbon pools at forest level (Source: Hendrick and Black, 2009)

As well as carbon sequestration in the growing forest, the long term storage of carbon in harvested wood products (HWPs) represents a well-recognised and very important carbon pool outside the forest. Substitution of fossil fuels with wood energy from sustainably managed forests is a further carbon mitigation opportunity. These three pathways are incorporated into the Forest Carbon Tool.  A further pathway, not included in the current system boundaries, is the substitution of energy intensive building materials such as concrete and steel with wood products. This can have a high level of impact in future years. For example, using one tonne of wood instead of concrete can lead to an average reduction of over 2.0 tonnes of CO2 emissions over the lifecycle of a product.

Forest Carbon Tool Development

Teagasc, in conjunction with the Department of Agriculture, Food and the Marine (DAFM) and (FERS) Limited, have developed an online Forest Carbon Tool (www.teagasc.ie/forestcarbontool). The Forest Carbon Tool is now available as a user-friendly way to get an indication of how much carbon can potentially be removed through various forest scenarios and through important pathways that help address our climate challenges. The tool provides indicative values and is not, at this stage, intended to provide definitive or absolute data on any particular forest or for processes related to forest carbon valuation or potential trading platforms. 

Users of the tool can select from a dropdown list of current planting options under the Forestry Programme (called Grant and Premium Categories or GPCs) or otherwise from selected forest species or species groups. They can then select an appropriate soil type and, upon hitting the calculate button, will get indicative values for mean yearly CO2 sequestration (t/CO2-eq/ha/yr) and mean cumulative sequestration values (t/CO2-eq/ha), the latter being an estimate of the (once off) maximum potential sequestration, termed the CAP value. Both of these are normalised metrics, derived over 2 forest cycles or rotations. As we know that the sequestration levels do not stay constant but change significantly over rotations, so the tool also graphically displays the annual sequestration trends over the two forest cycles. While growing forests capture and store CO2 during active growth, activities such as forest thinning and harvesting give rise to emissions which the tool also takes into account.

Using the tool

Outputs from the tool indicate that mean annual sequestration rates (under the current assumptions described) can range from 1-9 tonnes of CO2 per hectare per year and are influenced by the tree species, forest age and soil types entered. Today’s Signpost Webinar presented some examples of outputs from the Forest Carbon Tool. Application of the tool can provide a useful support mechanism to help inform decision making in terms of forest establishment and management. It shows that all forest types can have an important role to play in helping address climate change.

Figures 2-4 provide summary examples of mean annual and mean cumulative sequestration (CAP value) for GPC 8, GPC 3 and GPC 11 planting categories. Broadleaf forests (e.g. alder, birch), while having a lower mean annual rate of carbon capture, also tend to have a high sequestration potential as indicated by CAP value (figure 2).  Productive conifer species (e.g. GPC 3, figure 3) such as spruce can return high sequestration rates, especially when their harvested wood products are taken in account. Agroforestry, which combines trees and continued agricultural activity on the same land, can provide sequestration capacity while also countering emissions from livestock such as sheep, as indicated in figure 4.

Figure 2 - GPC 8 – Fast growing broadleaves e.g. alder and birch with 15% area retained for biodiversity enhancement on a suitable mineral soil

  • Mean annual CO2 sequestration – 3.46 t/CO2-eq/ha/yr
  • Sequestration potential - 471 tCO2-eq/ha

 

Figure 3: GPC 3 – 70% spruce (by area), 15% broadleaf species, 15% area retained for biodiversity enhancement (ABE - open space, hedgerows and retained habitat) on a mineral soil

  • Mean annual CO2 sequestration - 6.8 t/CO2-eq/ha/yr
  • Sequestration potential - 357 t/CO2-eq/ha

 

Figure 4: GPC 11 Agroforestry – Fast growing broadleaves e.g. sycamore on a mineral soil  combined with grazing for sheep between rows of trees (7 ewes per hectare)

  • Mean annual sequestration1.68 t/CO2-eq/ha/yr
  • Agricultural emissions – 1.18 t/CO2-eq/ha/yr
  • Sequestration potential - 251 tCO2-eq/ha

Users of the Forest Carbon Tool are requested to become familiar with the range of assumptions involved as well as the scope for future enhancements. The objective of this first iteration is to provide high level indicative information on the capacity of forests to sequester carbon and particularly provide some insights for users on the comparative merits of different forest planting options.

The Forest Carbon Tool also provides useful awareness raising and decision support functions, providing indicative data on the role of different planting options and their capacity to contribute to farm level carbon mitigation. There is also an ongoing need to further develop our knowledge on the impact of a range of factors such as forest types, species choices, rotation lengths and management approaches on sequestration potential. To this end, it is anticipated that updates and enhancements can be incorporated into future iterations of the tool as new data and research becomes available.

Finally, it is also important to re-emphasise that carbon sequestration is one of a range of important services provided by sustainably managed forests. These include timber production, water quality protection, landscape and biodiversity enhancement. Factors such as landowner’s objectives, tree species choices and forest management approaches are central to determining the specific mix of services that farm forests can provide.

The Forestry Carbon Tool can be accessed here